Retractor pretensioner assembly

ABSTRACT

A pretensioner assembly for motor vehicle belt restraint systems is provided. The pretensioner assembly includes a tube in fluid communication with a gas generator and a polymer rod disposed therein that travels in a first direction in response to actuation of the gas generator. The polymer rod is plastically deformable and engages a sprocket to rotate the sprocket in response to the travel of the rod, where rotation of the sprocket causes pretensioning. The rod has a non-constant cross-section along its length. The rod becomes locked after actuation to prevent travel in an opposite direction. The system further includes a seal member and slug member disposed between the rod and the gas generator, where the seal member is relatively flexible and the slug member is relatively hard.

FIELD OF THE INVENTION

The present invention relates generally to seatbelt restraint devicesfor restraining an occupant of a vehicle, and more particularly, todevices for pretensioning a seatbelt.

BACKGROUND OF THE INVENTION

Seatbelt restraint systems for restraining an occupant in a vehicle seatplay an important role in reducing occupant injury in vehicle crashsituations. Seatbelt restraint systems of the conventional so-called“3-point” variety commonly have a lap belt section extending across theseat occupant's pelvis and a shoulder belt section crossing the uppertorso, which are fastened together or are formed by a continuous lengthof seatbelt webbing. The lap and shoulder belt sections are connected tothe vehicle structure by anchorages. A belt retractor is typicallyprovided to store belt webbing and may further act to manage belttension loads in a crash situation. Seatbelt restraint systems which aremanually deployed by the occupant (so-called “active” types) alsotypically include a buckle attached to the vehicle body structure by ananchorage. A latch plate attached to the belt webbing is received by thebuckle to allow the belt system to be fastened for enabling restraint,and unfastened to allow entrance and egress from the vehicle. Seatbeltsystems, when deployed, effectively restrain the occupant during acollision.

OEM vehicle manufacturers often provide seatbelt restraint systems withpretensioning devices, which tension the seatbelt either prior to animpact of the vehicle or even prior to impact (also known as a“pre-pretensioner”) to enhance occupant restraint performance. Thepretensioner takes out slack in the webbing and permits the beltrestraint system to couple with the occupant early in the crashsequence. One type of pretensioner acts on the webbing retractor totension the belt. Various designs of retractor pretensioners presentlyexist, including a type known as a roto-pretensioner that incorporates agas generator for generating a pyrotechnic charge. Examples of suchroto-pretensioners are described in U.S. Pat. No. 5,881,962, filed Apr.11, 1995, U.S. patent application Ser. No. 11/115,583, filed Apr. 27,2005, and U.S. patent application Ser. No. 12/830,792, filed Jul. 6,2010, which are commonly owned by the assignee of the presentapplication and are hereby incorporated by reference in their entiretyfor all purposes. Generally, ignition of the pyrotechnic charge or othercombustible material creates gas pressure in a chamber having a pistonto impart motion upon a driving element such as a piston, rack andpinion, or series of balls disposed in a pretensioner tube, which engagewith and wind a retractor spool sprocket to retract the webbing.

One issue with pretensioners using a series of metallic balls is theweight of the series of balls required for a full pretensioning stroke,as well as the corresponding cost of supplying multiple metallic ballswith strict tolerances. Further, for pretensioners using a series ofmetallic balls, or rack and pinion based systems, is the need for asynchronizing or clutch feature to ensure that the series of balls orpinion sufficiently engage the retractor spool sprocket.

Another issue with pretensioners is known as a low resistance condition,where the driving elements will reach an end of stroke withoutexperience substantial resistance. This can occur if there is excessiveslack in the seatbelt webbing. In these cases, the low resistanceresults in a lower amount of backpressure from the driving elements. Thebackpressure is produced by the engagement between the driving elementsand the sprocket, so lower backpressure reduces the pressure on asealing element that trails the driving elements. Reduced pressure onthe sealing elements reduces the amount that the sealing element iscompressed circumferentially. Reduced sealing ability can cause gas toleak from the tube around the series of balls.

A further issue with pretensioners is the need to maintain the retractorand the seatbelt webbing in a locked condition at the end of thepretensioning stroke. When the retractor spool does not remain locked,payback can occur which allows the seatbelt to unspool and reintroduceslack in the seatbelt. One method for maintaining the locked positionincludes maintain pressure from the gas generator beyond the amountneeded for the pretensioning stroke. However, this adds weight and cost.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a seatbelt retractor assembly for use ina passenger vehicle. The system includes a housing adapted for beingmounted to a vehicle structure; a tube having an arcuate and curvedshape having a first end in fluid communication with a gas generator andan exit in fluid communication with an interior cavity of the housing; asprocket rotatably mounted to the housing and fixedly coupled to aspindle adapted for taking up seatbelt webbing during pretensioning, thesprocket having a plurality of vanes; a curved guide of the housingdisposed on an opposite side of the sprocket from the exit of the tube;and a polymer rod disposed within the tube and having a non-constantcross-section with a main body portion and an enlarged portion. Thepolymer rod is plastically deformable. The polymer rod exits the tube,along a perimeter of the sprocket, and toward the curved guide inresponse to an actuation by the gas generator to rotate the sprocket andspindle to take up seatbelt webbing.

In another aspect of the invention, the polymer rod includes a proximalend and a distal end, wherein the proximal end is disposed toward thegas generator and the distal end is disposed away from the gasgenerator, and the enlarged portion is disposed at the proximal end forreceiving a load in response to actuation of the gas generator.

In another aspect of the invention, a seatbelt retractor assembly foruse in a passenger vehicle is provided. The system includes a housingadapted for being mounted to a vehicle structure; a tube having anarcuate and curved shape having a first end in fluid communication witha gas generator and an exit in fluid communication with an interiorcavity of the housing; a sprocket rotatably mounted to the housing andfixedly coupled to a spindle adapted for taking up seatbelt webbingduring pretensioning, the sprocket having a plurality of vanes; a curvedguide of the housing disposed on an opposite side of the sprocket fromthe exit of the tube; and a polymer rod disposed within the tube. Thepolymer rod is plastically deformable. The polymer rod exits the tube ina first direction, along a perimeter of the sprocket, and toward thecurved guide in response to an actuation by the gas generator to rotatethe sprocket and spindle to take up seatbelt webbing. The polymer rodbecomes locked against translation in a second direction that isopposite the first direction.

In another aspect of the invention, the assembly includes a seal memberand a slug member that are disposed between the polymer rod and the gasgenerator.

In another aspect of the invention, the tube includes a constrictiondisposed adjacent the exit of the tube.

Further objects, features, and advantages of the invention will becomeapparent to those skilled in the art to which the present inventionrelates from consideration of the following description and the appendedclaims, taken in conjunction with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is perspective view of an occupant restraint system;

FIG. 2 is a perspective view of the occupant restraint system withvarious components removed to show a seat belt retractor andpretensioner system;

FIG. 3 is a perspective view of the seatbelt retractor assembly;

FIG. 4 is a cut-away view of the pretensioner system illustrating atube, a rod, and a sprocket in a first, non-actuated position;

FIG. 5 is a perspective view of the rod;

FIG. 6 is a plan view of the sprocket having a plurality of vanes;

FIG. 7 is a side view of the sprocket;

FIG. 8 is a partial view of the sprocket illustrating the shape of thevanes;

FIG. 9 is a cross-sectional view of a gas generator, a seal, a slug, andthe rod of the pretensioner system in the first, non-actuated position;

FIG. 10 is a cross-sectional view of an alternative embodiment of theseal and slug;

FIG. 11 is a cross-sectional view of an alternative embodiment of theseal and slug;

FIG. 12 is a cross-sectional view of the pretensioner system in anactuated position;

FIG. 13 is a cut-away perspective view of a housing of the pretensionersystem illustrating one-way teeth for locking the rod after actuation;

FIG. 14 is a cross-sectional view of one embodiment of the one-wayteeth;

FIG. 15 is a cross-sectional view of another embodiment of the one-wayteeth;

FIG. 16 is a cut-away perspective view of a constriction in the tube ofthe pretensioner system;

FIG. 17 is a cross-sectional view of another embodiment of theconstriction;

FIG. 18 is a cross-sectional view of another embodiment of theconstriction;

FIG. 19 is a cross-sectional view of another embodiment of theconstriction;

FIG. 20 is a cross-sectional view of the seal expanded circumferentiallyto seal against the tube during actuation of the pretensioner system;and

FIG. 21 is a cross-sectional view of the seal and plug being restrictedby the constriction and the seal expanded circumferentially to sealagainst the tube during actuation of the pretensioner system.

FIG. 22 is a cross-sectional view of an alternative embodiment of theseal and slug.

It should be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

DETAILED DESCRIPTION OF THE INVENTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure or its application or uses.

Referring now to the drawings, FIG. 1 shows a vehicle seat 10 and a seatbelt assembly 12. The seat belt assembly 12 includes a seat belt webbing14 having a shoulder belt portion 16 extending from an upper guide loopor anchorage 18 to a latch plate 20 and a lap belt portion 22 extendingfrom the latch plate 20 to an anchorage 24. The latch plate 20 caninclude a loop portion 26 through which the webbing 14 extends. Thelatch plate 20 is able to be inserted into a seat belt buckle 28 to lockand unlock the seat belt assembly 12. A seat belt buckle cable 30,either directly or in cooperation with other components, secures theseat belt buckle 28 to a portion of the vehicle frame. It will beappreciated that other manners of attaching the seat belt webbing 14 tovehicle could also be used, including variations on the latch plate 26and the buckle 28 and their attachments to the webbing 14 and associatedvehicle structure.

The seat belt webbing 14 is able to pay-out from a retractor 32 assembly(shown in FIGS. 2 and 3), which is located within the vehicle seat 10(in an integrated structural seat design) or is coupled structurally tothe vehicle body, so that the effective length of the seat belt webbing14 is adjustable. When the buckle latch plate 26 has been fastened tothe seat belt buckle 28, the seat belt assembly 12 defines a three-pointrestraint between the upper anchorage 18, the buckle latch plate 26, andthe anchor point 24. Any other suitable configurations, such asalternative locations for the retractor assembly 32, the buckle latchplate 26, and the anchor point 24, may be used with the presentinvention.

Now with reference to FIG. 2, an isometric view of the seat beltassembly 12 of the present invention is illustrated disassociated fromthe motor vehicle and showing the spool retractor assembly 32. Theretractor assembly 32 includes a spool assembly 34 and a gas generator36 mounted to a common frame 38. The spool assembly 34 is connected withand stows the webbing 14 of the shoulder belt portion 16, whereas theend of the lap belt portion 22 of the webbing 14 is fixedly engaged withthe anchorage point, for example, the frame 38 or another portion of themotor vehicle such as the seat 10 or floorpan.

As best shown in FIG. 3, the spool assembly 34 includes a belt spool 40which engages the shoulder belt portion 16 of the webbing 14 and rotatesto wind-up or pay-out the belt webbing 14. A torsional “clock” or“motor” type spring is carried within a spring end cap 42 androtationally biases the spool 40 to retract the webbing 14. The spoolassembly 34 may further incorporate other spool control mechanisms whichare known in accordance with the prior art, including pretensioners,inertia and webbing sensitive locking devices, torsion bar loadlimiters, or other belt control devices. “Spool control systems”referred to in this specification may include any system which controlsthe rotational movement of a webbing spool, thus controlling theextraction and retraction of seat belt webbing. One such spool controlsystem is a motor-assisted retractor. Spool locking devices typicallyincorporate an inertia sensitive element, such as a rolling ball orpendulum, and cause a sprocket of the spool to be engaged to preventfurther withdrawing of webbing from the spool 40. Webbing sensitivelocking devices sense rapid pay-out of webbing to lock the retractor.Various electronic sensing mechanisms which detect the withdrawal ofwebbing and/or the connection of the tongue 26 to the buckle 28 may alsobe incorporated into the retractor assembly 32.

During normal operation of the vehicle, the retractor assembly 32 allowspay-out of seat belt webbing 14 to give the occupant a certain amount offreedom of movement. However, if an impact or a potential impactsituation is detected, the retractor assembly 32 is locked to preventpay-out and to secure the occupant in the seat 10. For example, if thevehicle decelerates at a predetermined rate or if the brakes areactuated with a predetermined force, then the retractor assembly 32 islocked. Due in part to the free pay-out of the seat belt webbing 14, theseat belt assembly 12 often develops slack during normal use.

The retractor assembly 32 further incorporates a pretensioner system 44(shown in FIG. 4) operatively connected to the spool assembly 34 andoperable to rotate the spool 40 for pretensioning. As known to those ofskill in the art, a retractor pretensioner winds seat belt webbing intoa more taught condition against the occupant at the initial stages of adetected vehicle impact. This is provided to reduce forward motion orexcursion of the occupant in response to the deceleration forces of avehicle impact or rollover.

The pretensioner system 44 includes a pretensioner tube 52 incommunication with the gas generator 36. The gas generator 36 is used toprovide expanding gas in response to a firing signal. As is known in theart, for example, the vehicle includes a sensor array sending a signalindicative of an emergency event such as an impact event, crash, orrollover. The vehicle sensor may be a specific impact sensor, or may bea traditional vehicle sensor (e.g. a longitudinal or lateralacceleration sensor) or otherwise part of a control system having asuite of multiple sensors. Any other impact sensor that is or will beknown to those skilled in the art may also be readily employed inconjunction with the seat belt assembly 12 of present invention. Anelectronic control unit such as a central processing unit (CPU) or othercontroller receives a signal and controls the seat belt assembly 12 torespond by tightening the seatbelt of the vehicle (e.g. via activationof a pretensioner).

FIG. 4 provides a cut-away illustration of the pretensioner system 44.The pretensioner tube 52 has a pretensioner rod 53 disposed therein(also shown in FIG. 5) that has an elongate shape and is flexible withinthe tube 52. More specifically, the rod 53, when disposed outside of thepretensioner tube 52 prior to insertion therein, has a generallystraight shape, and when inserted into the tube 52 it will bend and flexin accordance with the tortuous shape of the tube 52.

Turning now to the retractor assembly 32, the assembly 32 includes thespool assembly 34 mounted to the common frame 38, as described above.More particularly, the spool assembly 34 will rotate relative to thecommon frame 38 to wind the webbing 14 attached to the spool assembly34. The common frame 38 includes a housing 54 for housing the componentsof the pretensioner system 44.

The spool assembly 34 includes a sprocket 56 that is disposed within thehousing 54. The sprocket 56 is attached to the belt spool 40. Rotationof the sprocket 56 will cause the attached belt spool 40 to rotate towind the webbing 14 that is attached to the belt spool 40.

As shown in FIG. 5, the rod 53 has a generally circular cross-section inone form. In another approach, the rod could have a non-circularcross-section, such as a rectangular cross-section, triangularcross-section, or other polygonal cross-section that allows the rod 53to be inserted into the tube 52 and adapt to the tortuous shape of thetube 52 when inserted. The polygonal cross-section could rotate alongthe length of the rod 53 to create a spiral shape, in one approach.Additionally, or alternatively, the rod 53 could include protrusions,such as longitudinal rails or circumferential rings, or recesses, suchas longitudinal or circumferential grooves.

The rod 53 preferably includes a main body portion 62 that extends alonga majority of its overall length. The rod 53 further includes anenlarged portion 64 at one end. In one form, the enlarged portion 64 isin the form an enlarged diameter, but could also be in the form of anenlarged perimeter for a rod having a polygonal cross-section. Forpurposes of discussion, the rod 53 will be discussed as having acircular cross-section, such that the enlarged portion 64 is in the formof an increased diameter.

The rod 53 further includes a tapered portion 66 that extends betweenthe main body portion 62 and the enlarged portion 64, such that there isa gradual transition between the main body portion 62 and the enlargedportion 64. It one approach, the tapered portion 66 is in the form of astraight taper, such that a longitudinal cross-section of the taperedportion 66 would illustrate a constant slope. In another form, thetapered portion 66 could have a curved shape, such as a convex shapefacing outward from the rod 53, or a concave shape facing outward. Inanother approach, the tapered portion 66 could have a complex curvaturehaving both a convex and concave curvature.

The rod 53 includes a proximal end 68 that is disposed toward the gasgenerator 36 when the rod 53 is installed within the pretensioner system44. The rod 53 further includes a distal end 70 that is disposed at theopposite end of the rod 53 from the proximal end 68, with the enlargedportion 64 disposed at the proximal end 68.

The rod 53 is preferably made from a polymer material, which has areduced weight relative to metallic ball driving elements of otherroto-pretensioners. The particular polymer material can be selected tofit the particular desires of the user. The polymer material ispreferably one that has sufficient flexibility such that it can bend andflex through the tube 52 to allow for initial installation as well as inresponse to actuation by the gas generator 36. The polymer material ispreferably one that has sufficient pushability in response to actuation,such that the rod 53 will sufficiently transfer a load to a sprocket 56of the pretensioner system 44.

Further, the rod 53 is preferably made from a polymer material that isplastically deformable. During and after actuation, the rod 53 will bebecome plastically deformed in response to actuation and contact withother components of the pretensioner system 44. This plastic deformationwill be further discussed below with reference to the use of the system44, where the plastic deformation will cause the system to become lockedto prevent or limit payback of the rod 53 without being completelydependent on maintained pressure in the system.

In one approach, the rod 53 is made from a nylon thermoplastic material.The rod 53 could also be made from an aliphatic polyamide thermoplasticmaterial. In another approach, the rod 53 could be made from a similarthermoplastic material, such as an acetal material or polypropylenematerial.

It will be appreciated, however, that other materials for the rod 53could also be used that can activate the pretensioner 44 without plasticdeformation. For example, and elastically deformable material could beused, but such a material would not provide each of the advantages of aplastically deformable rod.

With reference to FIGS. 6-8, the sprocket 56 has a general annular shapethat defines an internal aperture 76. The sprocket 56 further defines aplurality of inward extending teeth 78 that extend into the aperture 76.The teeth 78 are sized and configured to correspond to recesses ordepressions that are defined on an external surface of the belt spool 40to connect the sprocket 56 to the belt spool 40 such that they arerotationally coupled. In another approach, the aperture could include asingle tooth or protrusion to rotationally couple the sprocket 56 to thebelt spool 40.

The sprocket 56 includes an annular body portion 80 and a flange portion82 that projects radially from the base of the body portion 80. Thesprocket 56 further includes a plurality of vanes 84 that each projectradially from body portion 80 as well as longitudinally from the flangeportion 82, such that vanes 82 extend between the body portion 80 andflange portion 82.

The vanes 84 each have a generally triangular shape when viewed from thefront, with a base that tapers into a point 86 as the vane 84 extendsradially outward from the body portion 80. The particular width andpitch of the vanes 84 can be selected as desired. The plurality of vanes84 combine to define cavities 88 that are disposed between adjacentvanes 84.

In one approach, each of the vanes 84 can have the same size and shapeand be uniformly distributed around the sprocket 56. In anotherapproach, the vanes 84 can have different sizes and/or be spaced atdifferent intervals. Adjusting the size and spacing of the vanes 84 canalter the amount of rotation and/or the rate of the rotation for thesprocket 84 when the pretensioner system 44 is activated. This variablesize and/or spacing is possible due to the actuation by the rod 53rather than by a series of similarly shaped balls. In a pretensionerthat uses a plurality of ball-shaped driving elements, the size andspacing is preferably uniform to account for the predetermined shape andsize of the balls.

In one preferred approach, the sprocket 56 includes 11 vanes 84. Thevanes 84 each have a height of 5.55 mm, and the cavities 88 accordinglyhave the same depth. The vanes 84 are evenly spaced around the diameterof the sprocket 56 with a spacing of approximately 32.73 degrees. Thevanes 84 have a taper angle of 30 degrees. The point 86 has an outerradius of 0.45 mm. Of course, other sizes could also be used.

In one approach, the cavities 88 have a complex curvature at their base.In this approach, the inner radius of the cavity 88 has twomeasurements. A first radius R1 is 2.8 mm, and a second larger radius R2is 4.3 mm. Accordingly, the corresponding vanes 84 have differentlengths of its sidewalls that remain straight before leading into thecurve of the base of the cavity 88.

The longer sidewall of the vane 84 on one side is directed toward therod 53 when the rod 53 is disposed within the tube 52. Accordingly, whenthe rod 53 travels toward the sprocket 56, the rod 53 will contact thelonger sidewall. One the opposite side of the vane 84, the sidewall isshorter because it will not directly contact the end of the rod 53.Instead, the shorter sidewall and larger radius that it leads into willresult in a wider and more robust base of the vane 84, thereby addinggreater resistance to deformation in response to the force from the rod53. This particular arrangement allows for a large landing area of therod 53 while maintaining a resistance to deformation.

With reference once again to FIG. 4, the housing 54 further include aguide portion 90. The guide portion 90 is disposed within the housing 54similar to the sprocket 56. More particularly, the guide portion 90 isdisposed opposite the exit of the tube 52, and the sprocket 56 isdisposed between the guide portion 90 and the tube 52. Accordingly, therod 53 exiting the tube 52 will contact the sprocket 52 prior tocontacting the guide portion 90.

The guide 90 has a generally arcuate landing surface 92 that has aconcave shape toward the exit of the tube 52. In one approach, the arcof the surface 92 has a constant radius. Further, the centerpoint of theradius of the arc is aligned with the rotational axis of the sprocket56, such that the radial spacing between the surface 92 and the sprocket56 is consistent along the length of the surface 92. In anotherapproach, the centerpoint of the radius of the surface could be offsetfrom sprocket axis, such that the radial spacing between the surface 92and the outer diameter of the sprocket 56 will vary at different pointsalong the surface 92.

The surface 92 includes a first end 96 and second end 98. The first end96 is disposed opposite the exit of the tube 52 such that the rod 53would engage the first end 96 prior to the second end 98 after exitingthe tube 52 and passing the sprocket 56.

The housing 54 further defines an overflow cavity 100 that is disposedopposite the guide 90. The overflow cavity 100 is also disposed adjacentthe curvature of the tube 52, and the sprocket 56 is disposed betweenthe guide 90 and the overflow cavity 100. Accordingly, an intermediateportion 102 of the guide 90 is diametrically opposite the overflowcavity 100 across the sprocket 56.

The overflow cavity 100 is sized and configured to allow a portion therod 53 to be received therein during actuation of pretensioner system44, if necessary. For example, after the rod 53 has exited the tube 52it will contact the guide 90 and be directed in an arcuate pathcorresponding to the guide 90, such that the rod 53 is ultimatelydirected toward the overflow cavity 100. The rod 53 can extend into theoverflow cavity 100, and can further be guided along the curvature ofthe tube 52 that is adjacent the overflow cavity 100. However, it willbe appreciated that the rod 53 may not necessarily travel far enoughduring actuation to ultimately reach the overflow cavity 100.

As described above, the retractor assembly 32 includes the gas generator36 that provides expanding gas in response to a firing signal. Theexpanding gas causes an increase in pressure within the tube 52, whichultimately causes the rod 53 to be forced away from the gas generator 36and through the tube 52.

More particularly, as shown in FIG. 9, the pretensioner tube 52 includesa piston or seal 102. The seal 102 can have a spherical shape with aspherical outer surface, in one approach. In another approach, the seal102 can have a generally cylindrical shape with a cylindrical outersurface, as best shown in FIG. 10. The seal 102 is slidably disposedwithin the tube 52 and is operable to drive the rod 53 along anactuating path A. As will be understood by those of skill in the art,the seal 102 may be press-fitted or otherwise fitted inside the tube 52.

As shown in FIG. 9, the seal 102 defines a proximal end 106 spaced fromthe gas generator 36 so as to define a gas chamber 108 therebetween. Theseal 102 defines a distal end 110 directed toward the rod 53.

In one approach, the pretensioner tube 52 includes a stopper ball orslug 112 disposed within the tube 52 between the seal 102 and the rod53. The slug 112 is preferably made from aluminum, but could be madefrom another suitable material of sufficient strength, such as steel orreinforced plastic. The slug 112 has a generally spherical shape in oneapproach. However, the slug 112 could have an ovular shape or generallycylindrical shape in other approaches. The slug 112 defines a proximalend 114 that is adjacent the distal end 110 of the seal 102, and adistal end 116 that is adjacent the rod 53.

In one approach, the seal 102 and slug 112 are two separate and distinctcomponents. In another approach, illustrated in FIG. 22, the slug 112could be integrated into the seal 102 such that are fixed to each other.In this approach, the slug 112 preferably has the same material strengthas described above, with the seal 102 being generally softer such thatit can provide the described sealing abilities. In this approach, theseal 102 and slug 112 are fixed via an adhesive, welding, mechanicalconnections, or the like.

The seal 102 and slug 112 cooperate to transfer the energy from theincreased pressure in the gas chamber 108 toward the rod 53. The rod 53,in order to travel through the tube 52 and flex according to thecurvature of the tube 52, is sized slightly smaller than the width ofthe tube 52. Thus, without the seal 102, gas from the gas generatorwould flow past the rod 53 in the space defined between the rod 53 andthe tube 52.

The seal 102 and slug 112 are sized to cooperate in a coupled manner. Inone approach, shown in FIG. 10, the proximal end 106 and the distal end110 of a seal 102′ having a cylindrical shape are each indented inwardso as to define semi-spherical recesses or concave depressions 118 and120. In this approach, the proximal end 114 of the slug 112 has a convexshape, such as the slug 112 having a spherical or ovular shape. Ofcourse, the slug 112 could be shaped similar to a bullet with the distalend 118 having a generally flat shape.

In another approach, shown in FIG. 11, the seal 102 could have aspherical shape, and the slug 112 could have a concave shape at itsproximal end 114. In another approach, the distal end 110 of the seal102 and the proximal end 116 of the slug 112 could both have convexshapes, as shown in FIG. 9, with the contact between the seal 102 andslug 112 occurring at a focused area where the convex shapes meet.

As will be discussed in greater detail below, the seal 102 defines agenerally elastic structure, and may be composed of various materialsknown in the art, such as any suitable plastic or polymer (e.g.,polyester, rubber, thermoplastic, or other elastic or deformablematerial). Moreover, the seal 102 may be die cast, forged, or moldedfrom metal, plastic, or other suitable material. In one aspect of thepresent invention, the seal 102 may be formed using a two-cavityinjection molding process. The generally elastic structure allows theshape of the seal 102 to change slightly in response to pressure,thereby improving the sealing that it provides.

In operation, the gas generator 36 produces expanding gas thatpressurizes the gas chamber 108, thereby enabling the seal 102 toforcibly drive the rod 53 along the actuation path A. As the rod 53driven through tube 52, it engages the sprocket 56. More particularly,the rod 53 engages the vanes 84 of the sprocket 56. Engagement of therod 53 with the sprocket 56 as the rod 53 is driven by expanding gas inthe direction of arrow A causes the spool 40 to rotate, which in turnprovides pretensioning. Of course, it should be understood that whilethe pretensioner system 44 employs the rod 53 for rotating the spool 40,the pretensioner system 44 may use alternative driving elements known inthe art, such as a plurality of balls or another type of flexible andpushable rod.

Activation of the gas generator 36 enables the seal 102 to resist gasleakage. As previously mentioned, the seal 102 is composed of arelatively elastic material. Therefore, pressurized gas within the gaschamber 108 causes the proximal end 106 of the seal 102 to expand, whichhelps prevent gas from escaping past the seal 102. In one approach, whenthe seal 102 has a cylindrical shape, the seal 102 includes a flexiblerim that expands circumferentially outward in response to pressurizedgas.

In addition, backpressure generated from the rod 53 causes the seal 102to expand circumferentially outward due to compression of the seal 102against the slug 112 and the rod 53. The rod 53 undergoes resistance asit engages the sprocket 56 during actuation, thereby generatingbackpressure on the slug 112 and the seal 102. This occurs regardless ofthe shape of the slug 112 and seal 102. In the case where the seal 102has a cylindrical shape, a distal rim defined by the seal 102 will alsoexpand radially outward. The circumferential expansion of the seal 102provides a tightened seal between the outer surface of the seal 102 andthe inner wall of the pretensioner tube 52. Accordingly, the seal 102 ofthe present invention is operable to retain a high seal pressure as wellas maintain residual gas pressure within the tube 52.

During actuation of a pretensioner and during pretensioning of theseatbelt there can be a side-effect known as payback, where the tensionon the seatbelt from caused by the occupant during an event triggeringpretensioning can rotate the spool in a direction opposite thepretensioning rotation. This rotation is transferred to the sprocket anddriving elements, causing the driving elements to travel in the reversedirection within the tube. Payback can be counteracted by maintainingpressure in the tube, but this requires the gas generator to fire for alonger period and additional propellant.

However, a preferred embodiment of the pretensioner system 44 describedherein includes features configured to counteract the above describedpayback side-effect as an alternative to or in addition to maintainedgas pressure. As described above, the rod 53 is preferably made of aplastically deformable material, such as a polymer.

With reference to FIG. 12, during actuation of the pretensioner system44, the rod 53 exits the tube 52 and contacts the vanes 84 of thesprocket 56, causing the sprocket 56 to rotate. As the rod 53 continuespast the sprocket 56 causing it to rotate, additional ones of vanes 84will contact the side of the rod 53, causing the rod to be compressedand deformed plastically in the area of interference between the vanes84 and the rod 53. This compression will also cause the rod 53 to becompressed against the guide 90, creating a press-fit configuration ofthe rod 53 between the sprocket 56 and the guide 90.

Additionally, the rod 53 and guide 90 are made from materials that willweld together at the end of the pretensioning stroke. For example, thematerials of the rod 53 and guide 90 are selected such that heatgenerated from the friction between the rod 53 and the guide 90 willcause the rod 53 and guide 90 to become welded together along aninterface W where the guide 90 and rod 53 contact each other. Once therod 53 and guide 90 are welded together, the rod 53 will become lockedand prevented or substantially limited from traveling back into the tube52. The plastic deformation of the rod 53 caused by the vanes willprevent or substantially limit the sprocket 56 from rotating in theopposite direction, thereby preventing or substantially limitingpayback.

The welding results from the relatively high heat and pressure generatedby the system during actuation. For the rod 53 and guide 90 to weld, thematerials used for each are preferably in the same family. For example,if the guide 90 is nylon, then the rod 53 is preferably nylon.Similarly, if the guide 90 is acetal, then the rod 53 is preferablyacetal. If the guide 90 is polypropylene, then the rod 53 ispolypropylene. It will be appreciated that other materials that willweld together under high heat and pressure could also be used. Moreover,it will be appreciated that some different types of materials can weldtogether.

With reference to FIG. 13-15, additionally, or alternatively, the guide90 can include a plurality of one-way teeth 120 formed on the surface ofthe guide 90. In one approach, the teeth 120 can be defined bydepressions 122 formed in the guide 90, as shown in FIG. 14. In anotherapproach, the teeth 120 can be in the form of protrusions 124 extendingfrom the guide 90, as shown in FIG. 15. In both instances, the teeth 120are oriented in a direction to allow the rod 53 to travel past the teeth120 during the pretensioning stroke, while limiting the rod 53 fromtraveling in the opposite direction, thereby preventing or substantiallylimiting payback. For example, when the rod 53 travels past one of theteeth 120, it will first pass over ridge or ledge 126, before passingover a gap 128. If the rod 53 is forced rearward, the rod 53 would beforced against the ridge or ledge 126, thereby preventing or limitingthe rod 53 from moving in that direction. Furthermore, the plasticdeformation of the rod 53 and the compressing force of the sprocket 56against the rod 53, forcing the rod 53 against the guide 90, will causeportions of the rod 53 to be pushed into the gap 128 formed by thedepression 122 or protrusion 124.

The one way teeth 120 can be used along with the welding describedabove, or could be used as an alternative if the materials selected forthe rod 53 and guide 90 will not weld. It will be appreciated that otherone-way mechanisms or structures could also be used in cooperation withthe rod 53 to limit payback.

Another side-effect that can occur during pretensioning is known as alow-resistance condition. This can occur when there is a relativelylarge portion of the webbing that can be taken up or wound by the spoolin response to actuating the pretensioner. For example, if there wasextra slack in the seatbelt, this slack would be taken up and wound withlower resistance because it would not be acting on the occupant untilthe slack was taken up. In a low resistance condition, the backpressureof the driving elements, whether in the form of balls or a rod oranother suitable driving element, is reduced. Reduced backpressure canresult in a reduced ability of the sealing element to expandcircumferentially against the inner wall surface of the tube in responseto the backpressure. This can occur for any type of piston or seal thatis configured to expand circumferentially in response to backpressure aspart of its sealing process.

With reference to FIGS. 16-21, to address the side-effect of alow-resistance condition, in one embodiment of the pretensioner system44, the tube 52 includes a constriction 130 disposed near the end of thetube 52 where the rod 53 exits. Of course, it will be appreciated thatthe constriction 130 could be used with other embodiments of apretensioner that use a plurality of balls rather than a rod. Furtherdiscussion of the constriction 130 will include references to the rod53, but it will be appreciated that such references can also apply toother driving element types, such as a plurality of balls, unlessotherwise noted.

The constriction 130 is in the form of a protrusion extending into thetube 52, thereby reducing the cross-sectional area of the tube 52 in adistinct location. The constriction 130 is sized such that there isenough space that the rod 53 can travel past the constriction 130, butthat the seal 102 and/or slug 112 will be blocked from travelling pastthe constriction 130. When the constriction 130 blocks the slug 112 andthe seal 102, the constriction 130 provides additional backpressure.Accordingly, the seal 102 will circumferentially or radially expand inresponse to this backpressure, thereby providing an improved seal inlow-resistance conditions. This improved sealing will prevent or limitthe potential for gas to escape from the tube in low-resistanceconditions.

The constriction can be formed in a variety of ways and have a varietyof shapes while providing the above described functionality. In oneapproach, shown in FIG. 16, the constriction 130 is in the form of abump 132 in the tube 52, such that the sidewall of the tube 52 maintainssubstantially the same thickness. The bump 132 is integrally formed withthe tube as a monolithic structure, at least in the area of theconstriction 130. Put another way, the bump 132 is not a separatecomponent or material attached to the tube 52. The bump 132 protrudesinto the tube 52, and has a corresponding depression 134 on an outersurface of the tube 52 (facing the overflow cavity 100, for example).The bump 132 has a convex shape within the tube 52 and the depression134 has a corresponding concave shape facing the overflow cavity 100.

In another approach, shown in FIG. 17, the constriction 130 could be inthe form of an increased thickness portion 138 that is integral with thetube 52. This is similar to the bump 132, but does not have acorresponding depression on outer surface of the tube 52.

In another approach, shown in FIG. 18, the constriction 130 is in theform a separate piece or crescent 136 that is attached to the tube 52within the tube 52. The crescent 136 can be attached via welding,adhesive, mechanical fasteners, or the like.

In another approach, shown in FIG. 19, the constriction 130 could be inthe form of a plate 140 that is inserted through an opening 142 formedin the sidewall of the tube 52. The plate 140 is removably insertedthrough the opening 142 and secured to the tube 52 via known securementmechanisms. In another approach, the plate 140 can be fixedly securedafter insertion through the opening 142. The use of the plate 140 allowsfor different shapes and sizes and materials to be easily selected andinstalled, if desired.

In the above approaches, the constriction 130 is preferably disposed onan inboard portion of the tube 52. Disposition of the constriction 130in this location allows for the rod 53 to slide across the outboardportion of the tube 52 during travel. The centrifugal force of the rod53 as it travels through the tube 52 will tend to force the rod 53toward the outboard portion of the tube 52, so locating the constrictionon the inboard portion reduces the potential for the constriction 130 toadd resistance to the rod 53. This applies to driving elements in theform of a plurality of balls, as well.

The above described constrictions 130 extend into a portion of thecircumference of the tube 52. However, a constriction could also extendinto the tube 52 around the entire circumference, such as in the form ofa circumferential rib.

As described above, the rod 53 has an enlarged portion 64 at itsproximal end, where the enlarged portion 64 has a larger diameter thanthe main body portion 62. In one approach, the enlarged portion 64 has adiameter that is larger than the width of the tube 52 at theconstriction 130. Accordingly, with the enlarged portion 64 disposedupstream of the constriction 130, the constriction 130 will prevent itfrom passing.

In another approach, the enlarged portion 64 can be smaller than thewidth of the tube 52 at the constriction 130. With the enlarged portion64 being small enough to pass the constriction 130, it can pass beyondthe constriction 130.

Having described the various above embodiments, the generalfunctionality of the system will now be described.

The pretensioner has a first, initial, or nominal state, in which therod 53 is positioned within the tube 52, as shown in FIG. 4. Theenlarged portion 64 of the rod 53 is preferably positioned within thetube 52 adjacent the seal 102 and slug 112. The seal 102 and slug 112are positioned upstream of the rod 53, with the slug 112 disposedbetween the seal 102 and the rod 53. The gas generator 36 is attached tothe end of the tube 52 so that the gas chamber 108 is defined betweenthe gas generator 36 and the seal 102.

In response to an event or signal that actuates pretensioning, the gasgenerator 36 will expel gas into the gas chamber 108. The increasedpressure within the chamber 108 will force the seal 102, slug 112, androd 53 away from the gas generator and along the path defined by thetube 52. The distal end 70 of the rod 53 will translate toward thesprocket 56, ultimately contacting one of the vanes 84 of the sprocket56. The force from the rod 53 exerted against the vane 84 will cause thesprocket 56 to rotate about its rotational axis, thereby ultimatelywinding the webbing 14 around the spool 40. At this point, the rod 53 isin a second, actuated position, relative to its initial, nominalposition. Of course, there are intermediate positions between the firstand second positions.

The enlarged portion 64 is initially positioned adjacent the seal 102and slug 112, as described above. In response to actuation of the gasgenerator 36, the force of the seal 102 and slug 112 is transferred tothe rod 53. This force will cause the proximal end 68 of the rod 53 tobe partially deformed in response. If the proximal end of the rod 53were a smaller diameter, the slug 112 could result in transferring theload to the rod 53 in an off-center position, resulting in a loss offorce. Thus, the enlarged portion 64 limits and reduces the potential ofoff-center loading.

The smaller diameter of the remainder of the rod 53 reduces its weightrelative to a rod 53 having a constant diameter, while still ensuringthat the load is not transmitted off-center. The smaller diameter of theremainder of the rod 53 also reduces resistance caused by frictionbetween the tube 52 and the 53 while the rod 53 is traveling through thetube 52.

Additionally, the enlarged portion 64 keeps the rod 53 centered withinthe tube 52 as it traveling through the tube 52 during actuation.

The rod 53 will continue being driven, such that it contacts the guide90 and is directed in an arcuate path corresponding to the shape of theguide 90. The rod 53 will continue to rotate the sprocket 56 as ittranslates along the guide 90. The distal end 70 of the rod 53 willultimately travel into the overflow cavity 100 and disengage from thesprocket 56, as shown in FIG. 12. The sprocket 56 will continue to bedriven by the engagement between the main body portion 62 of the rod 53and the sprocket 56. With the rod 53 partially disengaged with thesprocket 56, the rod is in a third position.

While in the third position, the rod 53 is prevented from moving in thereverse direction in embodiments that include the rod 53 and guide 90welding together at this position. Similarly, in embodiments having theone-way teeth 120, the rod 53 is similarly prevented from moving in thereverse direction. This is referred to as the locked position.

During actuation, the seal 102 and slug 112 will also travel along thetube 52, and the travel of these components assists in driving the rod53 through the tube 52. The seal 102 and slug 112 likewise have first,second, and third positions similar to the rod. In the second and thirdpositions, as well as the locked position of the rod 53, the seal 102and slug will experience backpressure from the rod 53 as it undergoesresistance contacting the sprocket 56 as well the guide 90. Thus, theseal 102 will have a circumferentially expanded state in the second andthird positions, as well as when the rod 53 is in a locked position, asillustrated in FIG. 20.

In embodiments or instances where the rod 53, or other driving element,travels along the path far enough, possibly due to a low-resistancecondition, the seal 102 and slug 112 will continue to travel through thetube 52 toward the constriction 130 (in embodiments that include theconstriction 130), where the slug 112 will ultimately contact theconstriction 130 at a fourth, constricted position, as shown in FIG. 21.The slug 112 will provide backpressure on the seal 102 in thisconstricted position, where the seal 112 will circumferentially expandto improve the sealing of gasses within the tube 52. In embodimentswithout the slug 112, the seal 102 would directly contact theconstriction 130 and similarly expand circumferentially in response tothe backpressure provided by the constriction.

A skilled artisan will appreciate that not all of the above features orcomponents must be used together. For example, the rod 53 can be usedwithout a welding configuration with the guide 90, the one-way teeth120, or the constriction 130. The constriction 130 could be used inpretensioners without the rod 53, the welding, or the one-way teeth. Forexample, the constriction 130 can be used in traditional pretensionersusing a series of balls as the driving element and still provide theimproved sealing in low-resistance configurations.

As a person skilled in the art will readily appreciate, the abovedescription is meant as an illustration of the implementation of theprinciples of this invention. This description is not intended to limitthe scope or application of this invention in that the invention issusceptible to modification, variation, and change, without departingfrom the spirit of this invention as defined in the following claims.

The invention claimed is:
 1. A seatbelt pretensioning retractor assemblyfor use in a passenger vehicle, the system comprising: a housing adaptedfor being mounted to a vehicle structure; a tube having an arcuate andcurved shape having a first end in fluid communication with a gasgenerator and an exit in fluid communication with an interior cavity ofthe housing; a sprocket rotatably mounted to the housing and fixedlycoupled to a spindle adapted for taking up seatbelt webbing duringpretensioning, the sprocket having a plurality of vanes; a curved guideof the housing disposed on an opposite side of the sprocket from theexit of the tube; a polymer rod disposed within the tube and having anon-constant cross-section with a main body portion and an enlargedportion, wherein the polymer rod is plastically deformable; wherein thepolymer rod exits the tube, along a perimeter of the sprocket, andtoward the curved guide in response to an actuation by the gas generatorto rotate the sprocket and spindle to take up seatbelt webbing; andwherein the curved guide includes a plurality of one-way teeth.
 2. Theseatbelt pretensioning retractor assembly of claim 1 wherein the polymerrod includes a proximal end and a distal end, wherein the proximal endis disposed toward the gas generator and the distal end is disposed awayfrom the gas generator, and the enlarged portion is disposed at theproximal end for receiving a load in response to actuation of the gasgenerator; and wherein the polymer rod includes a constant cross-sectionextending from an end of the enlarged portion to the distal end of thepolymer rod, wherein the enlarged portion has a solid cross-section. 3.The assembly of claim 1, wherein the one-way teeth permit translation ofthe rod from the tube in a first direction and limit translation of therod in a second direction opposite the first direction.
 4. The assemblyof claim 1, wherein the vanes of the sprocket plastically deform thepolymer rod in response to the polymer rod engaging the sprocket.
 5. Theassembly of claim 1, wherein the tube defines a passageway extendingtherethrough from the first end to the second end and includes aconstriction adjacent the exit of the tube, where the constrictionreduces a width of the passageway.
 6. The assembly of claim 1, furthercomprising a seal member disposed within the tube between the generatorand the enlarged end of the polymer rod, and further comprising astopper member disposed between the seal member and the polymer rod,wherein the seal member and the stopper member have a ball shape, andthe seal member has a greater diameter than the stopper member.
 7. Theassembly of claim 1, further comprising a seal member disposed withinthe tube between the generator and the enlarged end of the polymer rod,and further comprising a stopper member disposed between the seal memberand the polymer rod, wherein the seal member is made of rubber and thestopper member is made of aluminum.
 8. The assembly of claim 1, furthercomprising a seal member disposed within the tube between the generatorand the enlarged end of the polymer rod, and further comprising astopper member disposed between the seal member and the polymer rod,wherein the seal member and the stopper member are fixed to each other,the seal member comprising a rubber portion and the stopper membercomprising an aluminum portion, where the aluminum portion is disposedbetween the rubber portion and the polymer rod.
 9. The assembly of claim1, wherein the vanes each have a base portion that tapers down radiallyoutward and the base has a first radius on one side of the vane and asecond radius on the other side of the vane.
 10. A seatbeltpretensioning retractor assembly for use in a passenger vehicle, thesystem comprising: a housing adapted for being mounted to a vehiclestructure; a tube having an arcuate and curved shape having a first endin fluid communication with a gas generator and an exit in fluidcommunication with an interior cavity of the housing; a sprocketrotatably mounted to the housing and fixedly coupled to a spindleadapted for taking up seatbelt webbing during pretensioning, thesprocket having a plurality of vanes; a curved guide of the housingdisposed on an opposite side of the sprocket from the exit of the tube;a polymer rod disposed within the tube and having a non-constantcross-section with a main body portion and an enlarged portion, whereinthe polymer rod is plastically deformable; wherein the polymer rod exitsthe tube, along a perimeter of the sprocket, and toward the curved guidein response to an actuation by the gas generator to rotate the sprocketand spindle to take up seatbelt webbing; and wherein the polymer rodwelds to the curved guide in response to the actuation by the gasgenerator and translation of the polymer rod into engagement with thecurved guide at an interface, and the polymer rod and a portion of theguide along the interface are made of the same material, such that heatgenerated between the polymer rod and the guide at the interface locksand welds the polymer rod to the curved guide.
 11. The seatbeltpretensioning retractor assembly of claim 10, wherein the polymer rodincludes a proximal end and a distal end, wherein the proximal end isdisposed toward the gas generator and the distal end is disposed awayfrom the gas generator, and the enlarged portion is disposed at theproximal end for receiving a load in response to actuation of the gasgenerator; and wherein the polymer rod includes a constant cross-sectionextending from an end of the enlarged portion to the distal end of thepolymer rod, wherein the enlarged portion has a solid cross-section. 12.The assembly of claim 10, wherein the vanes of the sprocket plasticallydeform the polymer rod in response to the polymer rod engaging thesprocket.
 13. The assembly of claim 10, wherein the tube defines apassageway extending therethrough from the first end to the second endand includes a constriction adjacent the exit of the tube, where theconstriction reduces a width of the passageway.
 14. The assembly ofclaim 10, further comprising a seal member disposed within the tubebetween the generator and the enlarged end of the polymer rod, andfurther comprising a stopper member disposed between the seal member andthe polymer rod, wherein the seal member and the stopper member have aball shape, and the seal member has a greater diameter than the stoppermember.
 15. The assembly of claim 10, further comprising a seal memberdisposed within the tube between the generator and the enlarged end ofthe polymer rod, and further comprising a stopper member disposedbetween the seal member and the polymer rod, wherein the seal member ismade of rubber and the stopper member is made of aluminum.
 16. Theassembly of claim 10, further comprising a seal member disposed withinthe tube between the generator and the enlarged end of the polymer rod,and further comprising a stopper member disposed between the seal memberand the polymer rod, wherein the seal member and the stopper member arefixed to each other, the seal member comprising a rubber portion and thestopper member comprising an aluminum portion, where the aluminumportion is disposed between the rubber portion and the polymer rod. 17.The assembly of claim 10, wherein the vanes each have a base portionthat tapers down radially outward and the base has a first radius on oneside of the vane and a second radius on the other side of the vane. 18.A seatbelt retractor assembly for use in a passenger vehicle, the systemcomprising: a housing adapted for being mounted to a vehicle structure;a tube having an arcuate and curved shape having a first end in fluidcommunication with a gas generator and an exit in fluid communicationwith an interior cavity of the housing; a sprocket rotatably mounted tothe housing and fixedly coupled to a spindle adapted for taking upseatbelt webbing during pretensioning, the sprocket having a pluralityof vanes; a curved guide of the housing disposed on an opposite side ofthe sprocket from the exit of the tube; a polymer rod disposed withinthe tube and being plastically deformable; wherein the polymer rod exitsthe tube in a first direction, along a perimeter of the sprocket, andtoward the curved guide in response to an actuation by the gas generatorto rotate the sprocket and spindle to take up seatbelt webbing; wherein,in response to an engagement between the polymer rod and the curvedguide, the polymer rod becomes fixed to the curved guide and the polymerrod becomes locked against translation in a second direction that isopposite the first direction based on the engagement between the rod andthe curved guide; wherein the polymer rod is locked due to engagementwith one-way teeth of the guide.
 19. A seatbelt retractor assembly foruse in a passenger vehicle, the system comprising: a housing adapted forbeing mounted to a vehicle structure; a tube having an arcuate andcurved shape having a first end in fluid communication with a gasgenerator and an exit in fluid communication with an interior cavity ofthe housing; a sprocket rotatably mounted to the housing and fixedlycoupled to a spindle adapted for taking up seatbelt webbing duringpretensioning, the sprocket having a plurality of vanes; a curved guideof the housing disposed on an opposite side of the sprocket from theexit of the tube; a polymer rod disposed within the tube and beingplastically deformable; wherein the polymer rod exits the tube in afirst direction, along a perimeter of the sprocket, and toward thecurved guide in response to an actuation by the gas generator to rotatethe sprocket and spindle to take up seatbelt webbing; wherein, inresponse to an engagement between the polymer rod and the curved guide,the polymer rod becomes fixed to the curved guide and the polymer rodbecomes locked against translation in a second direction that isopposite the first direction based on the engagement between the rod andthe curved guide; wherein the polymer rod is locked in response to theactuation by the gas generator and translation of the polymer rod intoengagement with the curved guide at an interface, such that heatgenerated between the polymer rod and the guide at the interface locksand welds the polymer rod to the curved guide.